personally i find Delving Deeper an extremely clear and runnable version of OD&D - i've been using it "in anger" for a few years now, and have only made minimal mechanical changes. it represents a very clear and concise package. i think there is a huge amount of value in going through the original OD&D books and "working it out yourself" but more as a philosophical exercise rather than seeking something you can use right now to run a game.